The joints of a human body are subject to substantial stresses, and as people age, their joints often function less effectively than when they were younger. Injury and disease can also affect joint function. It is becoming increasingly common to replace natural joints in the human body with artificial ones when the natural joints wear out or no longer function properly. Artificial hips and knees are widely used, and other joints such as the elbow are also replaced on occasion.
Most artificial joints include a stem or anchor portion that is inserted into the bone on either side of the damaged joint and a pair of bearing surfaces at the protruding ends of the stems that interact with one another to form a joint. Various joints in the body are generally replaced with structurally similar artificial joints; thus a knee joint will generally be replaced with a hinge joint and a hip joint will be replaced with a ball-and-socket joint. In some cases, however, such as with elbow joints, it may be desirable to replace the natural joint with an artificial joint structurally different from the original joint to improve the function of the patient's joint. Thus a natural single-axis elbow joint is sometimes replaced with a prosthetic device that includes two pivotal axes. In this case, a stem embedded in an ulna connects to a central joint element at a first location and a stem embedded in a humerus connects to the central joint element at a second location spaced apart from the first location so that both posts pivot about different, normally parallel, axes. Such bi-axial elbow joints and the benefits and uses thereof are described in greater detail in U.S. Pat. Nos. 5,314,484 and 5,376,121 which patents are hereby incorporated by reference.
The type of replacement joint selected by a surgeon will depend on many factors including the age, health and activity level of the patient and the size and condition of the bones adjacent the joint being replaced. Unfortunately, it is often difficult to determine which of these joint types should be used until a patient's joint has been exposed during surgery. This is especially true in elbow replacement surgery where a the need for a double axis joint is often not evident until the damaged joint can be directly examined. Thus, a surgeon may need to obtain both types of joints prior to a surgery even though only one joint will be used. Because double-axis elbows are used less frequently that single-axis joints, and are also more expensive than single-axis joints, surgeons may tend to use a single-axis joint even in cases where a double-axis joint would be more appropriate. Moreover, because a surgeon may need to partially install or modify one of the artificial joints before determining that a different device would be preferable, it may be necessary to discard one of the two prostheses at a considerable cost.
It is known to provide certain types of prosthetic joints in kit form which kits include a plurality of different elements, some or all of which may be used to form a given joint depending on the condition of the natural joint as revealed by surgery. For example, U.S. Pat. No. 6,027,534 describes a modular elbow kit that includes three different bearing elements. A first element is used when the elbow joint is to be configured in a constrained mode and a second and third element are used instead of the first element when the joint is to function in an unconstrained mode. Beneficially, the same kit can be used in a wide variety of patients. Stocking identical kits is generally less expensive that stocking a variety of different prosthetics, and, as a majority of the items in each kit will be used in every surgery, waste is minimized.
It would be therefore be desirable to provide a kit for forming a prosthetic joint that could be assembled to produce either a single-axis joint or a double-axis joint.